Unbeknownst to her brother, the curious sister peeks through the keyhole, catching him in the throes of self-pleasure. His thick, engorged cock pulses in his fist, glistening with pre-cum. She watches, entranced, as he strokes himself to the edge, his moans muffled by the closed door. Her own hand finds its way between her legs, rubbing her damp panties as she witnesses his forbidden pleasure.